Environmental maps describing the mobile environment of autonomous mobile robots (hereinafter, simply called “mobile robots”) may be used in the mobile robots for their autonomous movements (see Patent documents 1-3). Such environmental maps are used for estimating for the self position of mobile robots in mobile environment and for planning of moving paths and the likes. For example, the environmental map is generated as a grid map, in which two-dimensional (2D) mobile environment, where the mobile robot moves, is divided in a grid pattern, and an indication to indicate whether or not the mobile robot can move is arranged in each grid cell framed in by grid lines.
The generation of environmental maps are implemented, for example, by measuring the mobile environment using a range sensor capable of obtaining range information of the outside world, such as a laser range finder and a stereo camera (see Patent documents 1, 3 and 4). The environmental maps may be generated in advance and then supplied to mobile robots, or may be generated by the mobile robots having range sensors in their own while moving in the mobile space. The latter technique in which the estimation of the self position of the mobile robot and the generation of the environmental map are performed simultaneously is called “SLAM (Simultaneous Localization and Mapping)”.
For example, a mobile robot disclosed in Patent document 1 is equipped with plural range sensors adopting different sensing principles, e.g., an ultrasonic sensor and an infrared sensor, and measures plural spatial areas located at different heights from the floor surface on which the mobile robot is located by using these range sensors. Then, the mobile robot disclosed in Patent document 1 generates plural 2D environmental maps based on range data obtained by the range sensors, and generates a single 2D environmental map by superimposing and integrating these plural 2D environmental maps. The mobile robot disclosed in Patent document 1 searches an optimal moving path that can avoid an obstacle by referring to the integrated 2D environmental map, and performs movement while avoiding the obstacle.
Furthermore, Patent document 2 discloses an environmental map for a mobile robot in which 2D mobile space is divided into unit areas. Then, with the environmental map being defined as an xy-plane, x-direction and y-direction distances from each unit area to an obstacle are recorded as information for each unit area. The mobile robot disclosed in Patent document 2 estimates the self position in the mobile environment by comparing a distance to an obstacle measured by a range finder with a distance to the obstacle recorded in that environmental map.
Furthermore, Patent documents 3 and 4 disclose techniques to generate environmental maps for mobile robots in which positions of obstacles are identified as 2D grid maps. Specifically, the mobile robots disclosed in Patent documents 3 and 4 measure mobile environment by a range sensor installed in the mobile robot, and project the position of an obstacle calculated by using the measured range information on a 2D grid map. When cells for which the number of times an obstacle is projected exceeds a predefined value, the cells are determined as “obstacle cells” in which an obstacle exists and an environmental map in which the positions of obstacles are specified is created.
[Patent Document 1]
Japanese Unexamined Patent Application Publication No. 2005-310043
[Patent Document 2]
Japanese Unexamined Patent Application Publication No. 62-58311
[Patent Document 3]
Japanese Unexamined Patent Application Publication No. 2006-252346
[Patent Document 4]
Japanese Unexamined Patent Application Publication No. 2001-242934